This invention relates to heat exchangers and more particularly to heat exchangers of the cross-fin type and to the method of making the same.
Cross-fin heat exchangers commonly in use are of two types, namely the plate-fin type and the side-entry type. In the plate-fin type of heat exchangers, the tubing forming the coil portion of the heat exchanger is inserted longitudinally through openings formed in the cross-fins of the heat exchanger in inwardly spaced relation to the marginal edges thereof. In side-entry type heat exchangers, the cross-fins thereof have notches formed in their marginal edge portions. The notches are aligned in rows and the tubing is inserted transversely into the aligned notches from row to row.
In known heat exchangers of both types, the fin assemblies comprise a plurality of separate fin strips arranged in an array with the longitudinal openings, or the transverse notches, aligned to receive the tubing. During assembly of such heat exchangers, it is necessary to support the fin assembly in a suitable jig while the tubing is being inserted. Although plate-fin type heat exchangers provide good thermal contact between the cross-fins and the tubing, a shortcoming is that the tubing must be inserted in sections and the sections interconnected at the ends by return bends which are soldered or otherwise connected to the tube sections which define the passes through the fin assemblies. On the other hand, in side-entry type of heat exchangers, the provision of the open-ended notches along the marginal edges of the fin assemblies enables use of a one-piece tube. However, because such heat exchangers have open-ended notches, the cross-fins cannot contact the tubing over its entire outer periphery. The peripheral contact is reduced by at least by the width of the open-end portion of the notch through which the tubing is inserted into the fin assembly. To maximize contact between cross-fins and tubing, it has been common practice in the manufacture of side-entry type heat exchangers to form the notches with an entry portion leading into a body portion, the entry portion being smaller in width than the body portion so that tubing slightly flattened transversely, may be inserted transversely through the entry portion into the body portion and then expanded. Such expansion both interlocks the cross-fins and tubing against removal and enables the tubing to engage the side walls of the body portions along a greater portion thereof.
The fin stock used in heat exchanger fin assemblies is typically of a thickness in the range of 0.007 to 0.010 inches. The size of the fin stock as well as the tubing size determine the overall dimensions of the heat exchanger assembly. Heretofore, in exchanger assemblies employing separate fin strips, the need for sufficient structural strength of the fin assembly dictated the size of the fin stock material and thus the overall size of the heat exchanger assembly. That is, the individual fin strips must be of sufficient thickness to allow the tubing to be inserted into the notches of the assembled fin strips without deforming the fin strips.